Method and a mixture for the preparation of an iron melt with a low sulphur content

ABSTRACT

(1) A method for the preparation of an iron melt with a low sulfur content wherein a mixture is added to the melt, the mixture comprising Na2CO3, calcium compounds and a quantity by weight of NaCl which is at least one-third and at most three times the quantity (by weight) of Na2CO3 while, of the total mixture, at least one-third consists of calcium compounds and (2) said mixture for adding to an iron melt.

United States Patent Inventors Appl. No.

Priorities l-lermanus Bakkerus Voorhurg;

Bernardus J. J. van der Holst. Delft. both of Netherlands Dec. 2, 1968 Nov. 9, l97l Nederlandse Organistle Voor Toegepast- Natuurweten-Schappelijk Onderzoek Ten Behoeve Van Nljverheid, Handel En Verkeer The Hague, Netherlands Dec. 5, 1967 Netherlands Nov. 6, 1968, Germany, No. P 18 07 322.0

METHOD AND A MIXTURE FOR THE PREPARATION OF AN IRON MELT WITH A LOW SULPHUR CONTENT 18 Claims, No Drawings US. Cl 75/55, 75/58, 75/l30 lnt.C| C2lc7/02 so new of Search 75/53. 58. I30. 55

[ 56! References Clted UNITED STATES PATENTS 2,75S,l80 7/l956 DeLaval 75/58 X 2,834,668 5/l958 Barnes l. 75/58 3,05 l ,564 8/1962 Drenning... 75/58 X 3,158,465 l l/l964 Brown 75/58 X 3.258.328 6/1966 Goss 75/53 X FOREIGN PATENTS 8 l 2,4l0 4/l959 Great Britain 75/53 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Joseph E. Legru A1!orneySpenccr& Kaye melt.

METHOD AND A MIXTURE FOR THE PREPARATION OF AN IRON MELT WITH A LOW SULPHUR CONTENT The invention relates to a method and a mixture for the preparation of an iron melt with a low sulfur content. Many For this purpose a mixture is introduced into the melt, the mixture consisting of Na,CO and at least one calcium compound, such as CaC and possibly CaO, to which, according to the invention, a quantity (by weight) of NaCl (at least oneiron ores, and fuels used for smelting these in a furnace, have a 5 third and at most three times the quantity of Na CO is high sulfur content, and attempts have been made to reduce added. Preferably equal amounts of NaCl and Na,CO are the sulfur content by adding substances while charging the furadded, but the amount of neither substance is more than that nace. Some of such added substances produce side effects on of the calcium compound(s).

other constituents of the melt, however, and many difficulties In order to minimize the generation of gas, less than one may also arise with the furnace lining and the slag. l fourth NaCl and less than one fourth Na,CO should be em- Preference is therefore given to desulfurizing outside the ployed in the mixture; the resulting slag can then be properly furnace, either by adding special agents to the stream of melt, removed and aggressiveness obviated. or by collecting the melt in special devices and desulfurizing it E llem res lts are Obtained if the sum of the amounts of in these, such as vibrating ladles or ladles with injection NaCl and z s does exceed One hir f he quantity of lances, stirring devices or dippers. These special devices are l the Calcium P Unlike z, h a mixture proexpensive and unsuitable for continuous operation, and the vides better desulfurization at a lower melt temperature than treatment must be continued for a fairly long time to obtain at a higher temperature; it can therefore also be used in desulthe desired desulfurization. furiling P g iron- Examples of desulfurizing agents for pig iron are Q a d These mixtures enable continuous addition without expen- CaC,. This desulfurization is not very effective or takes a very sive extra devices, the quantity of the mixture being relatively l ti because th l temperature i f i l small and not giving rise to attack or dangerous gas genera- Na,CO;, is also used as a desulfurizing agent, but it is very tion- While the slag moreover. is y to removeaggl'essive and attacks ningi Preferably, not more than 20 kg. mixture is added per ton of II is know" use a mixture of C and z a which is melt because this amount can already lead to desulfurization blow" with a lance into a ladle in the form of fine granules 25 of over 40 percent, with both an initial sulfur content of 0.2 suspended in nitrogen or air, in amounts of from l0 to 25 kg. and 0 04 percent. per ton of melt. In larger amounts, it makes the slag unworka- The f yj mixture can also be added to the melt with Me, and a large Percentage of z a in the mixture results in the aid of conventional devices, such as in a ladle with a lance, a y Severe altack the lining- 3 an agitator, or a dipper or in a vibrating ladle. Desulfurization According to another method, in addition to about 17 kg. of calcium compounds, such as CaO and CaF 2 to 7 kg. of Na CO per ton of melt is added to a bath. This bath is then agitated for a number of minutes with the aid of a lowfrequency electric current.

takes place more quickly than usual, and higher desulfurization percentages are possible.

Some examples of mixtures added to a stream of melt, and the results obtained with them are mentioned in the following tables.

NorE.1=Very little gas generation; 2=Very little gas; 3=Much gas; 4=Very much gas; a=Vcry easy slag removal; b=Easy slag removal; c=Difficult slag removal; d=Very difficult slag removal.

For Thomas steel a desulfurizing method is known accord- In these cases the mixture was added to the stream of melt,

ing to which per ton of melt about 5 kg. Na CO and 2 kg. Na CO 'I'I O are added in addition to CaC This reaction produces very large amounts of gas and is dangerous.

The desulfurizing agent used for cast iron, which has a higher temperature than pig iron, is mainly CaC,. It is expensive and does not work quickly. Its use, moreover, may adversely increase the carbon content of the melt. According to one method blocks of CaC are melted on the melt bath in a ladle by means of an electric arc, and NaCl is used as a flux in the slag. Finally, a mixture of CaC and NaCl may be introduced in the form of a briquette into the ladle by means of a dipper. The quantities used generally do not exceed 25 kg. per ton of melt, whereas the reaction time is fairly long.

The object of the present invention is a method whereby an inexpensive desulfurizing mixture with a very short reaction time so that it can be introduced into the melt without any adverse effects, for instance by adding it on or in the stream of melt.

and the final sulfur percentage was determined immediately after deslagging.

Table A shows that CaC, alone has hardly any effect in this short time. Addition of N a CO considerably increases the desulfurization percentage but the slag becomes more difficult to work, while the aggressiveness of the Na,CO continues to exist and the lining is attached.

Addition of NaCl to the mixture according to the invention results in an improvement of desulfurization while the slag can be worked better and gas generation remains within reasonable limits. Replacement of all the Na CO by NaCl makes the slag unworkable, and also entails considerable gas generation, while the desulfurization percentage is considerably reduced.

On the whole, the best result is obtained with approximately equal amounts of Na CO and NaCl.

Tests were next made to ascertain how effective a mixture in accordance with the invention is with low sulfur contents, and what quantity is advisable.

TABLE B Kg./ton melt S, percent Desulphur- Total kg./t0n izatlon, melt CaCz NazCOi NaCl Initial Final percent Notes 1 1 0.047 0.025 47 1a 2.5 2.5 10.4 0.022 45 2b 3. 3.75 0.04 0.022 45 3b 5 5 0.04 47 3c.

TABLE C Kg./tn melt S, ercent Desul hur- Total kg./ton p izz tion, melt CaCz NazCOa NaCl Initial Final percent Notes 20.. 15 2.5 2.5 0.2 0.085 57.5 2b 30.. v.....-.. 22.5 3.75 3.75 0.2 0.07 65 3b 40 30 5 0. 2 0. 065 67. 5 30 TABLE D Desulphurization KgJton melt I f 1 S S after percentage altermi 121 Total kgJton melt CaC Na CO NaCl percent 1 min. 3 min. 8 min. 1 min. 8 min TABLE E Kg./ton melt S, percent Desplpliiur- Z 011, NazCOa NaCl Initial Final percent Notes 16 1a 2 59 42 la 1 0.111 0. 05 55 1a 1 1 0. 090 0. 043 56. 5 1a 1. 5 1. 5 0.107 0. 045 58 2b 2. 5 2. 5 0. 1 0.042 58 2b 5 5 0. l 0. 04 60 3c 3. 75 3. 75 0. l 0. 042 58 3b 5 5 0. 1 0. 04 60 30 TABLE F Total KgJton melt S, percent DesulphurkgJton ization. melt CaC; Na CO NaCl Initial Final percent Notes 18 0.082 0. 050 28 1,570 C 18 0.091 0.078 14 1.450" C 2. 5 2. 5 0.116 0.061 48 1,600 C 15 .2. 5 2. 5 0.104 0.052 50 1,540 C 15 2. 5 2. 5 0. 097 0. 041 56 l.450 C TABLE 0 Kg./ton melt Dcsulphurlzatlon, Total kgJton melt CaC, Na Co NaCl percent l Determined after approximately minutes.

TABLE H S. percent Desulphurlzatlon Alter percentage Kg.'ton melt lnltlal 1 min. S. lmmeagitalimnv- Alter Total kgJton melt CaO CflCg N e 0 0; NaCl percent dintely tion diatsly 1 mm.

15. 15 0. 094 0.085 10 20. l0 10 0,004 0.072 23 20... 15 2. 5 .5. 5 0. 102 0.072 0. 050 51 20. 10 5 2. 5 Z. 5 0.110 0.061 0.037 45 66 20... 5 10 2. 5 2. 5 0.086 0. 042 0.023 51 73 17.. 5 l0 1 l 0. 107 0. 050 0. 38 45 65 20. 15 2. 5 2. 5 0. 102 0.058 0 H45 43 Table B shows that a quantity of more than 30 kg. per ton of melt, containing one-eighth Na,CO and one-eighth NaCl. provides little improvement in desulfurization, but gives rise to increasing drawbacks as regards the generation of gas and with regard to the slag.

In order to ascertain whether the mixture is also effective for high sulfur contents, and what quantity is then advisable. the following tests were carried out.

Again, a quantity of more than 30 kg. per ton of melt proves to offer no advantage.

Desulfurization with the mixtures is effected in a short time Tests were carried out m which the sulfur content was determined after 1 minute. after 3 minutes and after 8 minutes. The mixture was not introduced In the stream of melt but was added to a small amount of melton the bottom of the ladle.

after WhlCh the ladle was immediately filled with melt. No agitation in the ladle was applied.

The quantities of mixture in fact caused no serious drawbacks as regards gas and slag.

Equal amounts of the three substances do give a savll'lg in CaC,, but dcsulfunzation declines compared with a mixture containing less Na CO and NaCl The mam desulfurlzation effect IS already reached after 1 minute however. and is equal to or higher than desulfurrzation with Cat, after 8 minutes For cast iron melts contalnlng about 0 1 percent sulfur, the minimum amounts of NaCl and Na CO and the maximum quantity of mlxture of the best composition compared with CaC only were also determined Preferably. not more than l0 kg. Na,CO;,+NaCl should be added. More than 25 kg. mixture per ton of melt does not improve the result. Less than 1.5 kg. Na CO +NaCl seems to have little result as regards cast iron, the more so as the saving in CaC is then unimportant.

The above-mentioned tests were all conducted at a melt temperature of about l450 C. It is known that when CaC is used at a higher melt temperature, the desulfurization percentage increases. With a mixture of three-fourth CaC oneeighth Na,CO and one-eighth NaCl the desulfurization percentage surprisingly rises as the temperature is reduced.

As with a cast iron melt, the preferred mixture results in greater desulfurization at a lower temperature than at a higher temperature, a number of tests were carried out with pig iron, which has a much lower temperature. The mixture was introduced into a ladle holding 25 tons, the bottom of which was covered with pig iron, and the ladle was filled with pig iron in two to three minutes. The quantity of the mixture was very small but gas generation was great. The slag was crumbly to firm, but easy to remove. With continuous addition to the stream gas generation is much slighter.

As CaC may give rise to the increase of the carbon content in the melt under certain conditions, it was ascertained whether there would also be any advantage in using a mixture according to the invention also with CaO or mixtures of CaC and CaO.

As CaO acts more slowly than CaC,, the mixture was introduced in subsequent tests along with the stream of cast iron into the ladle and the sulfur content was determined once immediately and once more after the contents of the ladle had been agitated for 1 minute.

Addition of equal amounts of Na CO, and NaCl thus gives an immediate and very great improvement in all cases, while a further improvement is effected later because the CaO continues to work for some time.

In this case, of course, agitation is an additional complication.

We claim:

1. A mixture for desulfurizing a sulfur-containing iron melt outside a furnace, consisting essentially of (a) Na CO (b) NaCl and (c) a material, each component of which is a desul furizing calcium compound; the weight of NaCl being at least one-third and at most three times the weight of Na CO and the material comprising at least one-third of the mixture.

2. A mixture according to claim 1 wherein the material consists essentially of calcium carbide.

3. A mixture according to claim 1 wherein the material comprises a calcium compound selected from the group consisting of CaC and CaO.

6 4. A mixture according to claim 3 containing equal amounts of NaCl and Na CO 5. A mixture according to claim 3, less than one-fourth of which consists of NaCl.

6. A mixture according to claim 3, less than one-fourth of which consists of Na CO 7. A mixture according to claim 3 wherein the sum of the weights of NaCl and Na CO; is at most one-third the weight of the material.

8. In a method for reducing the sulfur content of a sulfurcontaining iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim I.

9. In a method for reducing the sulfur content of a sulfurcontaining iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim 2.

10. in a method for reducing the sulfur content ofa sulfurcontaining iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim 3.

11. A method according to claim 10 wherein the mixture contains equal amounts of NaCl and Na cO 12. A method according to claim 22 wherein at least one of NaCl and Na CO comprises less than one-fourth of the mixture.

13. A method according to claim 10 wherein the sum of the amounts of NaCl and Na CO in the mixture is not more than one-third of the quantity of the calcium compound content thereof.

14. A method according to claim 10 wherein the mixture is continuously added along with the stream of melt.

15. A mixture according to claim 1 wherein the material consists essentially of at least one member selected from the group consisting ofCaC, and CaO.

16. In a method for reducing the sulfur content of a sulfurcontaining iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim l5.

17. A method according to claim 16 wherein the mixture contains equal weights of the sodium chloride and of the sodium carbonate.

18. A method according to claim 16 which comprises introducing the mixture into a stream of said melt before the melt enters a ladle.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,619,171 Dated November 9th, 1971 Inventor(s) Hermanus Bakkerus and Bernardus J.J. van der Holst It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 8, change "Organistie" to -Organisatie-; line 16, change "P 18 07 322.0" to P 18 07 332.0. Column 1, line 52, change "Na CO 'H O" to Na CO -lOH O-. Column 2, line 57, change "attached" to attacked; in Table B, the second amount in the column under "Initial" should be changed from "10.4" to -0. 4. Table D, at the top of the second column, change "Ca? to --CaC at the top of the third column, change "Na CO to Na CO Column 3, line 71, after "time" insert a period Column 4, line 67, after "NaCl" insert a period line 69, after "minutes" insert a period line 70, change "0 l" to -O.l; line 73, after "determined insert a period Column 6, line 24, change "22" to l0-; line 32, change "10" to 8--.

Signed and sealed this 2nd day of May 1972.

(SEAL; Attest:

M. FLETCHER, J R attesting Officer ROBERT GOTTSCHALK Commissioner of Patents USCOMM-DC 50376-l=69 GOVERNMENT wnmrwc OFFICE i969 o3s6-33-1 

2. A mixture according to claim 1 wherein the material consists essentially of calcium carbide.
 3. A mixture according to claim 1 wherein the material comprises a calcium compound selected from the group consisting of CaC2 and CaO.
 4. A mixture according to claim 3 containing equal amounts of NaCl and Na2CO3.
 5. A mixture according to claim 3, less than one-fourth of which consists of NaCl.
 6. A mixture according to claim 3, less than one-fourth of which consists of Na2CO3.
 7. A mixture according to claim 3 wherein the sum of the weights of NaCl and Na2CO3 is at most one-third the weight of the material.
 8. In a method for reducing the sulfur content of a sulfur-containing iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim
 1. 9. In a method for reducing the sulfur content of a sulfur-containing iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim
 2. 10. In a method for reducing the sulfur content of a sulfur-containing iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim
 3. 11. A method according to claim 10 wherein the mixture contains equal amounts of NaCl and Na2CO3.
 12. A method according to claim 22 wherein at least one of NaCl and Na2CO3 comprises less than one-fourth of the mixture.
 13. A method according to claim 10 wherein the sum of the amounts of NaCl and Na2CO3 in the mixture is not more than one-third of the quantity of the calcium compound content thereof.
 14. A method according to claim 10 wherein the mixture is continuously added along with the stream of melt.
 15. A mixture according to claim 1 wherein the material consists essentially of at least one member selected from the group consisting of CaC2 and CaO.
 16. In a method for reducing the sulfur content of a sulfur-containing iron melt by adding a composition to the melt, the improvement wherein the composition is the mixture according to claim
 15. 17. A method according to claim 16 wherein the mixture contains equal weights of the sodium chloride and of the sodium carbonate.
 18. A method according to claim 16 which comprises introducing the mixture into a stream of said melt before the melt enters a ladle. 